The linkage between riparian predators and aquatic insects across a stream-resource spectrum

1. Spatial subsidies, defined as the flow of energy, nutrients, organisms or pollutants from one habitat to another, have been shown to affect the food–web dynamics in a wide range of ecosystems. An important subsidy to riparian communities is the contribution of adult stream insects to terrestrial predators such as birds, bats and lizards, but also invertebrates including ground and web‐building spiders. 2. We surveyed 37 first‐ and second‐order forest streams across differing environmental gradients in the Central South Island, New Zealand, to investigate the relationship between potential aquatic prey subsidies and predatory riparian arachnids. We anticipated that stream‐insect biomass would be positively associated with riparian arachnids, as a result of emergent adult aquatic insect subsidies to the adjacent habitat. 3. We confirmed positive associations between stream‐insect biomass as a predictor variable and riparian arachnid biomass (R² = 0.42, F_1,34 = 25.2, P < 0.001) and web densities (R² = 0.45, F_1,14 = 11.5, P < 0.01) respectively as dependent variables after adjusting for the confounding effects of environmental variables. Hierarchical partitioning confirmed the importance of stream insect biomass as a statistically significant contributor to the total explained variance in analyses calculated for arachnid biomass, abundance and web density. 4. A concurrent survey of spider‐web density along 20‐m transects from the stream edge into the forest indicated a strong decline in web‐building spider density moving away from the stream (R² = 0.41, F_1,158 = 109, P < 0.001), with stream‐insect biomass as a significant covariate (F_1,149 = 17.7, P < 0.001). 5. Our results suggest that productivity gradients present in the donor system affect the magnitude of the interaction between adjacent habitats. Productivity gradients may lead to increased reciprocal subsidies through a positive feedback loop involving the predation of spiders and other predatory terrestrial invertebrates by aquatic predators. However, terrestrial insectivores such as birds, bats and lizards that are not readily used as prey by aquatic predators may circumvent the feedback cycle by consuming a large proportion of emergent aquatic‐insect biomass. This may lead to asymmetry in the strength of food–web linkages between aquatic and terrestrial habitats.     

How Political Connections Affect Corporate Environmental Performance: The Mediating Role of Green Subsidies

This study investigates the relationship between political connections and corporate environmental performance, and examines the role of government green subsidies on this relationship within the current Chinese context. Using data from publicly traded private manufacturing firms, empirical results show that politically connected firms are significantly more likely to obtain green subsidies than non-connected firms. Assisted by green subsidies, firms with political connections show better environmental performance than those without. Our findings reveal the mechanism by which corporate political connections influence environmental performance.     

Factors affecting the fate of Pacific lamprey carcasses and resource transport to riparian and stream macrohabitats

1. Anadromous fish transport marine-derived nutrients to freshwaters during spawning migrations with potential implications for stream food webs. While many studies have explored the role of marine-derived nutrients instream ecosystems (particularly via Pacific salmonids [Oncorhynchus spp.]), relatively few have examined the spatial distribution and patchiness of non-salmonid fish carcasses or rates of transport to the riparian zone.
2. We radio-tagged and released 144 mature Pacific lamprey (Entosphenus tridentatus) prior to spawning and tracked the fate of post-spawn carcasses in two inland Columbia River basin streams to characterise spatial distribution of carcasses and marine-derived nutrient deposition. We found that 27 and 40% of lamprey that could be assigned a fate were moved into the riparian zone adjacent to stream segments exhibiting higher velocity conditions with larger substrates. Conversely, lamprey with instream fates were associated with depositional microhabitats and woody debris dams. Estimated carcass loading rates varied by more than an order of magnitude among habitats. These patterns probably reflect a combination of processes influencing the likelihood of carcass removal (e.g. by predators or scavengers, or stranding) and factors affecting the distribution of carcasses remaining within the stream.
3. Our results demonstrate substantial transport of lamprey carcasses across the stream-riparian ecotone and a non-random distribution of carcasses within streams, patterns which probably influence how resources enter stream and riparian food webs. More broadly, the results suggest local and landscape-scale hydrogeomorphic factors, along with species-specific traits and phenology, affect the distribution and potential roles of fish carrion in stream food webs.